Failback causes lost lease

[Sean McMurray]

Gregory,

Thanks for your reply.

On 06/25/2015 12:47 PM, Gregory Sloop wrote:
> Re: Failback causes lost lease *SM> In testing my dhcp failover, I 
> pulled the ethernet cable on the primary
> SM> server.
>
> SM> The secondary server acknowleged renewal requests as expected.
>
> SM> Then I plugged the cable back in. After both the primary and secondary
> SM> had moved from communications-interrupted to normal, the secondary 
> logs
> SM> multiple dhcp requests from a client whose lease is owned by the 
> primary
> SM> server. The primary server does not log any of these but the last
> SM> request, reporting that "lease in transition state expired".
>
> SM> Then the secondary server logs a DHCPDISCOVER from that client and
> SM> records it load balancing to the primary server.
>
> SM> The primary server also sees the DHCPDISCOVER and offers a new lease
> SM> that is not the same number as the previous lease. This despite 
> the old
> SM> number not having been reassigned.
>
> SM> The end result is that failback causes my clients to change their ip
> SM> address.
>
> SM> Why does this happen and how can I prevent it?
>
> SM> _______________________________________________
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> *SM> dhcp-users at lists.isc.org <mailto:dhcp-users at lists.isc.org>
> SM> https://lists.isc.org/mailman/listinfo/dhcp-users 
> <https://lists.isc.org/mailman/listinfo/dhcp-users>
>
> 1) Logs would be good.
> 2) I think something with your config is broken. If I were to [wildly] 
> guess, it's a physical/network layer issue.
> 3) I have a very small setup with 100+ clients, and it certainly 
> doesn't work this way for me.
>
> There are some issues when a single server is up and in 
> "communications interrupted" mode and you've got a tight IP pool and 
> the leases were fairly evenly balanced against both servers. [I've 
> posted, in the past, about an event that was kinda ugly for this 
> client while running a 4.1 version [IIRC]. *However* those problems 
> should be vastly less of a problem with 4.2+ - and you're not having 
> an issue with communications interrupted anyway.
I am having an issue with communications interrupted. When I pull the 
ethernet cable, both the primary and secondary servers move from normal 
to  communications-interrupted.

As far as "tight IP pool" goes, it's the only ip in use in a /16 pool.
>
> IIRC, you had a problem where the two servers wouldn't recover from CI 
> to Normal like they should too. How did you solve that problem? Is it 
> possible this is related? [I'm too lazy to go check old threads, but I 
> _think_ it was you...my apologies if I'm wrong.]
That was a stupid networking mistake where the failover traffic wasn't 
making it between peers. That problem was solved when I quit being so 
stupid. In this case, the peers are communicating failover data 
correctly when not in "communications-interrupted" stage.
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